ABSTRACT Among the most devastating causes of non-traumatic hemorrhage are the Filoviruses, including Ebola and Marburg. Fatality rates from hemorrhage by infection with either of these viruses can exceed 90%. Their outbreak potential was underscored by the 2013-2016 Ebola epidemic in West Africa, which grew from one infected toddler to over 28,000 cases and claimed ~11,000 lives. In acute filovirus infections, patients often develop endothelial leakage and disseminated intravascular coagulation. This vascular disruption, combined withseverediarrheaandvomiting,canprogresstoprofoundhypovolemia,hepaticandrenalfailure.Ebolaand Marburg viruses express a single surface glycoprotein (GP) required for host cell infection. Following macropinocytoticuptake,filovirusinfectionoccursbyGPbindingtodomainCoftheendosomalNiemann-Pick C1 (NPC1-C) receptor. The ZMapp antibody cocktail is one proposed treatment for Ebola virus, but to date therearenoapprovedsafeandeffectiveantibodyorsmallmoleculeinhibitorsforanyotherfilovirusinfection. Toaddresstheneedforimprovedtreatmentoptionsforthesepathogens,Iwillusestructure/functionanalysis tocharacterizethemechanismoftwopromisingclassesoftherapeuticcandidatesthatblockreceptorbinding andarebroadlyreactive.ThefirstclassconsistsofneutralizingantibodiesfromahumanMarburgsurvivorthat block infection by binding conserved receptor-binding sites on GP. MR191 and MR72 are both potent monoclonalantibodiesthattargetMarburg,butMR72isuniqueinitsbroadfiloviruscross-reactivity.LastyearI determined the crystal structure of MR191 in complex with Marburg virus GP and grew crystals of a MR72- MARV GP complex. Here, I propose to solve the MR72-GP complex structure, and compare antibody-GP contactstodeterminecriticalinteractionsitesandhowMR72achievescross-reactivity.SinceMR191showed lifesavingpotentialinnonhumanprimatesandisapossibletherapeuticforhumans,IwillalsoevaluateMR191 escapemutants,whichcouldbeusedtoassessitspotentialagainstemergentviralstrains.Thesecondclass includessmallmoleculecompoundstargetingtheNPC1receptor.Iwilldeterminestructuresoftwocandidate small molecule inhibitors in complex with NPC1-C, and use Ebola GP and other filovirus GPs pseudotyped ontoVesicularStomatitisVirustoassesswhetherthesecompoundsinhibitviralentry.Inthisfocusedresearch plan,IwillthususecrystalsandreagentsalreadyinhandtoapproachtreatmentofEbolaandMarburgvirus diseasefromtwoangles:immunotherapyagainstthereceptor-bindingsiteandsmallmoleculetherapyagainst the receptor. This work will be critical for understanding the inhibitory mechanisms of these therapeutic molecules, and will help guide development of safe and effective therapeutics for future outbreaks. This proposalwillcomplementmyclinicaltraininginglobalinfectiousdiseaseinSanDiegoandUganda.